1. Technical Field
This invention relates to control loading, and, more particularly, to an improved control loading system for use in vehicle and aircraft simulation systems employing digitally controlled linear electro-magnetic actuators in place of conventional hydraulic actuators.
2. Background Information
Various types of control systems exist for the control of the major flight operating components of modern aircraft. Depending upon the size and type of aircraft, such control systems vary from a yoke or stick connected to a mechanical cable linkage to the latest control technology termed "fly-by-wire". The majority of aircraft control systems, both commercial and military, are based upon a combination of electrically controlled hydraulic actuators. The control loading system provides the pilot of the aircraft with the ability to control aileron, elevator and other aircraft control elements with an artificially induced "feel" for the action produced. This "feel" for controlling the major components, (i.e., rudder, aileron, elevator) is extremely important in that it provides a constant tactile feedback to the pilot. For instance, if a pilot traveling at Mach 2 operates the rudder, the dynamic pressure placed upon the rudder makes any attempt in rudder change a manual effort. This physical effort can prevent excessive rudder changes at high speeds. In an aircraft simulator, the control loading system must accurately reproduce this "feel" in all simulated flight regimes for the control stick, yoke, and pedals.
Flight simulators are widely used and accepted today because they provide the capability and fidelity to safely and effectively train flight crew members in the execution of normal, abnormal and emergency operating procedures. Situations such as engine-failures can be created in the flight simulator, which would not be prudent or practical to attempt in the actual aircraft. Further, simulators reduce the need for non-revenue training flights and conserve aviation fuel.
Today's sophisticated flight simulators trace their genealogy back to the grounded flight trainers developed by Edwin A. Link, Jr. in the 1930's. Over the years, aircraft simulators have become more and more technically sophisticated. Modern day simulators are driven by computer and are often mounted on synergistic 6 degree-of-freedom motion systems. Fiberglass shells are often used to reproduce the exterior profile of the flight deck; with interior equipment, often actual aircraft parts, supported from said shell so as to exactly duplicate the interior of the cockpit, including the control stick (or yoke) and rudder pedals are employed.
Critical to the simulator is the need for a realistic control system that provides the pilot with control training but further provides a realistic "feel" of aircraft operation. Prior art control loading systems used in simulators parallel actual aircraft operation by the use of simulator hydraulic systems which replicate the actual forces on the control components throughout the flight envelope. Analog and digital control loops based on hydraulic fluid pressure are used. Obvious problems in using a hydraulic system within flight simulators include hydraulic leaks, hydraulic lines and pumps, and costly hydraulic actuators.
The use of electrical rotary motors has also been attempted with flight simulators. The rotary motors suffer from error inducing force ripples due to fixed, wound-wire poles and provide relatively low torque which must be geared to produce usable forces, giving poor accuracy in the proper feel. U.S. Pat. No. 3,463,866 issued to Staples discloses a control loading system using a servo feedback loop in combination with a digital computer. The disclosure sets forth a flight control system that is simulated with hardware which is slaved to a servo for feedback to the simulator. An electrical and hydraulic flight control system is disclosed in U.S. Pat. No. 4,227,319 issued to Bernard Guy et al., providing a hydraulic piston actuator which when moved a distance by the pilot's controller creates a servo signal which represents part of a reaction force opposing the control force generated.
The present invention eliminates the problems associated with hydraulic and rotary electrical control loading systems through the use of a digitally controlled linear electrical actuator that can be accurately programmed to correlate to numerous different aircraft.
Although especially useful for flight simulators, the principles of the invention could be used in other vehicle simulators and in actual aircraft control systems.